1. Field of the Invention
The present invention relates to a server system for storing and reproducing information and a method for delivering information from the server and for storing information in the server. More particularly, the invention concerns the server system and the delivering and storing method for dealing with continuous signals such as video signals. The invention also relates to the server system and the delivering and storing method capable of being simultaneously used at arbitrary timing through plural terminal units.
2. Related Background Art
The following describes the technology for storing or reproducing information, as described in Japanese Laid-open Patent Application No. 3-58348 filed prior to the present application by the applicant of the present invention.
FIG. 13 is a conceptual drawing of the above prior art. Reference numeral 1301 designates a system controller for controlling this information recording and/or reproducing device. Numeral 1302 is a crossbar switch for switching connection between three input/output routes 1304 to 1306 and three optical disks 1307 to 1309 each for storing/reproducing information. Numeral 1303 indicates a management table for the system controller 1301 to refer to for control of crossbar switch 1302 and control of reading/writing with each optical disk, which stores the status of each optical disk.
A continuous signal supplied through the input/output route 1304 is given destination addresses changed in order by the crossbar switch 1302 and is recorded as distributed as partial signals in the respective optical disks 1307 to 1309. Reproduction of the signals recorded in the optical disks is also carried out by reading the partial signals recorded in the respective optical disks. At this time the crossbar switch also switches connection in a predetermined order so as to continuously supply the partial signals outputted from the respective optical disks to one input/output route.
Another conceivable configuration is a server system for delivering signals by use of a switching system for carrying out the ordinary arbitration control. A prior art switching system of this type will be described below.
FIG. 14 shows a crossbar type switching system having N input terminals and N output terminals as a first example of switching system. In FIG. 14 numeral 87 denotes decoders, each of which reads an address part of a packet and informs the control unit of an output terminal to which this packet should be directed. Numeral 88 represents FIFOs (First In First Out), each of which temporarily stores an input packet and outputs it in the input order to an output line according to control from the control unit. Numeral 89 indicates input lines for supplying a packet signal outputted from the FIFO to an input of switch. Numeral 90 denotes switches, each of which serves as a switch of whether or not a packet signal supplied to an input line is to be outputted to an output line. Numeral 91 represents the control unit, which performs the reading control of each FIFO and the control of opening/closing of each switch, according to the output from the decoders. Numeral 92 indicates output lines, each of which supplies a packet signal outputted from the switch, to an output terminal.
In this crossbar type switching system, the control unit performs the routing control for changing the output terminal to be selected for output, by controlling opening/closing of switches connected to a desired output terminal. The control unit also carries out the arbitration control; when the so-called output contention occurs as inputs from plural input terminals simultaneously request outputting to one output terminal, the control unit executes the arbitration control for determining which input out of these plural inputs is to be outputted. The switching operation is achieved based on these controls.
This first example of switching system, however, had a drawback that the scale of hardware became very large, because, in the case of the N input terminals and N output terminals, N.times.N switches were necessary.
In this first example of switching system, N outputs of switches for connection between plural input lines and output lines are connected to one output line. This results in long wiring of connection lines, which causes occurrence of wiring delay, increase of stray capacitance of wiring, and so on. Increase of the number N of input terminals would make it difficult to increase the operating speed of switch. Therefore, this first example of switching system has a drawback that it is not suitable for quick switching of input packet signal.
In addition, this first example of switching system includes a need for carrying out the arbitration control while detecting occurrence of output contention as to inputs from the all input terminals, for every output terminal. Therefore, it had a drawback that the scale of hardware of the control unit for this control increased.
FIG. 15 shows a second example of switching system for overcoming the drawbacks of the first example of switching system described above. In this example the switching system is configured of switches of 2.times.2 having two input terminals and two output terminals, described below, connected in multiple stages. In FIG. 15 numeral 93 to numeral 104 represent the switches of 2.times.2 with two input terminals and two output terminals, which have two functions, straight connection for connecting the input terminals with the output terminals straight and cross connection for connecting the input terminals with the output terminals in a crossing manner. These twelve switches of 2.times.2 are connected in a shuffle network pattern, thereby realizing an omega switching system with eight input terminals and eight output terminals.
FIG. 16 is a structural diagram to show the inside of the switch of 2.times.2 with two inputs and two outputs described above. In FIG. 16 numerals 105 and 106 denote decoder I and decoder II, each of which reads an address part of an input packet and informs the control unit of an output terminal to which this packet is to be outputted. Numerals 107 and 108 represent FIFO I (First In First Out) and FIFO II, each of which temporarily stores an input packet and outputs it in the input order to a selector, based on the control from the control unit. Numerals 109 and 110 indicate selector I and selector II, each of which selects an FIFO storing a packet signal to be outputted to an output destination, based on the control from the control unit. The aforementioned straight connection is a state in which the selector I selects the FIFO I while the selector II selects the FIFO II; the aforementioned cross connection is a state in which the selector I selects the FIFO II while the selector II selects the FIFO I.
In this second example of switching system, the number of switches 2.times.2 necessitated is NlogN-N/2 (wherein the base of log is 2), which is smaller than N.times.N in the first example. The second example, however, necessitates the decoders, FIFOs, control unit, and selectors for each switch of 2.times.2, and thus had a drawback that the scale of hardware as a whole became large. Furthermore, this second example of switching system had a problem that even in case of connection being not from different input terminals to one output terminal, the so-called blocking phenomenon that connection to a desired output destination was not achieved, occurred depending upon circumstances of connection of the other input terminals. Specifically, for example when the input terminal 5 is connected with the output terminal 3 in FIG. 15, the switch 93 of 2.times.2 is set in the crossing state, and blocking occurs in connecting the input terminal 1 with the output terminal 1, because the switch 93 of 2.times.2 has to be set in the straight state.
The switching systems with the electrical switches as shown in the first and second examples of switching system had a drawback that they required use of elements capable of switching at high speed for high-speed operation and such high-speed electric elements were very expensive so as to increase the cost of the total system. Under such circumstances switching systems in the configuration for performing switching after converting a packet signal to an optical signal have been and are studied as quick switching systems of packet signal.
An example of this type is a third example of switching system in which a switching system of 8.times.8 is constructed by connecting optical switches of 2.times.2 of an optical waveguide type having the same functions as in the second example of switching system described above, in multiple stages by use of optical fibers. FIGS. 17A and 17B are a schematic diagram and a cross-sectional view of an InP based total reflection type optical switch, which is one of crossing type optical switches being optical switches of 2.times.2 of the optical waveguide type, used in the third example of switching system. The operation of the InP type total reflection type optical switch is such that carriers are injected into the crossing part where two optical waveguides cross, so as to change the refractive index of a refractive index varying region, whereby an optical signal incident to the crossing part is transmitted or totally reflected to effect switching. This index change by carrier injection is based on the band filling effect that the index change becomes greater as the wavelength of incident light approaches the wavelength of absorption edge of band-to-band transition.
The current injection into the index varying region is effected by the carrier confining effect by a p-InP cladding layer and an n-InP substrate having a large band gap and current constriction by a Zn diffusion region. An InGaAsP cap layer is provided for obtaining good ohmic contact with the electrode. The optical switches are demanded to reduce transmission losses of optical signals and to have large extinction ratios (or to decrease crosstalk). The index change needs to increase for increasing the extinction ratios. The optical switch described above is the one using the band filling effect, and increase of transmission loss and increase of index change occurs as the wavelength of incident light approaches the absorption edge wavelength. Accordingly, setting of the wavelength of incident light is a determining factor for selection between a choice of decreasing the index change at the sacrifice of increase of crosstalk in order to reduce the transmission loss and a choice of increasing the index change to decrease the crosstalk while permitting increase of transmission loss. Setting of wavelength is thus difficult. Especially, when the switches of 2.times.2 are connected in multiple stages, the number of stages cannot be made large because of this tradeoff between the problem of transmission loss and the crosstalk. There was thus the problem that a large-scale switching system was not available. Since the response speed of switching of switch is limited by the lifetime of injected carriers, there is a problem that switching cannot be made at high speed.
FIGS. 18A and 18B show a fourth example of switching system, which is an example of switching system with eight input terminals and eight output terminals comprised of eight variable wavelength transmitting units of from I to VIII using tunable laser diodes (TLDs) and eight receiving units of from I to VIII using photodiodes (PDs). In FIGS. 18A and 18B numeral 112 to numeral 119 designate decoder I to decoder VIII, each of which reads an address part of an input packet and informs the control unit of an output terminal to which this packet is to be outputted. Numeral 120 to numeral 127 denote FIFO (First In First Out) I to FIFO VIII, each of which temporarily stores an input packet and outputs it in the input order to a variable wavelength transmitting unit, based on the control from the control unit. Numeral 128 to numeral 135 represent variable wavelength transmitting unit I to variable wavelength transmitting unit VIII, each of which converts a packet signal outputted from FIFO I to FIFO VIII to an optical signal of a predetermined wavelength, based on control of a wavelength control unit in the control section, and outputs the optical signal to a star coupler. Numeral 136 is the star coupler, which has a function to combine all beams of wavelengths outputted from the eight variable wavelength transmitting units and outputting the combined beams to eight filters. Numeral 137 to numeral 144 indicate filter I to filter VIII, each of which has a function to transmit only an optical signal of a fixed wavelength but intercept optical signals of the other wavelengths. The transmitting wavelengths of the respective filters are so set that the filter I is at .lambda.1, filter II at .lambda.2, filter III at .lambda.3, filter IV at .lambda.4, filter V at .lambda.5, filter VI at .lambda.6, filter VII at .lambda.7, and filter VIII at .lambda.8. Numeral 145 to numeral 152 stand for receiving unit I to receiving unit VIII, each of which has a function to convert an optical signal of a predetermined wavelength supplied through the filter I to filter VIII into an electric signal by the photodiode and outputs the electric signal to an output terminal. Numeral 153 denotes the control section for controlling the switching operation of this switching system, which is composed of an arbitration control unit and a wavelength control unit. The arbitration control unit performs control of output contention between input packets entering the respective input terminals for every output terminal to which each input packet should be outputted, based on an instruction supplied from each decoder. The arbitration control unit informs the wavelength control section of the result of this arbitration. The wavelength control unit controls a transmission wavelength of each variable wavelength transmitting unit, based on an instruction from the arbitration control unit. Since in this fourth example of switching system the eight filters I to VIII are so set as to transmit the different wavelengths of optical signals, the wavelengths of optical signals received by the respective receiving units are different from each other and thus independent. Therefore, the routing function for changing the output terminal to which the signal is to be outputted can be realized by changing the transmission wavelength of each variable wavelength transmitting unit.
This fourth example of switching system, however, needed to perform the arbitration control of packets supplied through the all input terminals en bloc, which increased the load in the arbitration control unit and which obstructed increase of speed of switching system.
In addition, the wavelength control unit needs to control the transmission wavelengths to the predetermined wavelengths every packet, according to the instruction from the arbitration control unit. For example, in the case wherein a packet is first sent at the shortest wavelength and the transmission wavelength of a packet to be sent next is the longest wavelength, a change amount of transmission wavelength of variable wavelength transmitting unit thus becomes large.
This requires quick wavelength control, which increases the scale of hardware; or the time necessary for the wavelength change becomes long, which was a drawback to obstruct the increase of speed of switching system.
In the video server system and the video delivery control method using the switching system as described above, the system needed to have the function for packeting the partial video signals to be delivered and the function for reproducing the partial video signals from the packets on the receiving side, which resulted in drawbacks of increasing the hardware scale and increasing the cost.